Catheters for imaging, sensing electrical potentials, and ablating tissue

ABSTRACT

An acoustic imaging system for use within a heart has a catheter, an ultrasound device incorporated into the catheter, and an electrode mounted on the catheter. The ultrasound device directs ultrasonic signals toward an internal structure in the heart to create an ultrasonic image, and the electrode is arranged for electrical contact with the internal structure. A chemical ablation device mounted on the catheter ablates at least a portion of the internal structure by delivery of fluid to the internal structure. The ablation device includes a material that vibrates in response to electrical excitation, the ablation being at least assisted by vibration of the material. The ablation device may alternatively be a transducer incorporated into the catheter, arranged to convert electrical signals into radiation and to direct the radiation toward the internal structure. The electrode may be a sonolucent structure incorporated into the catheter, through which the ultrasound device is arranged to direct signals. An acoustic marker mounted on the catheter emits a sonic wave when electrically excited. A central processing unit creates a graphical representation of the internal structure, and super-imposes items of data onto the graphical representation at locations that represent the respective plurality of locations within the internal structure corresponding to the plurality of items of data. A display system displays the graphical representation onto which the plurality of items of data are super-imposed.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/086,523, filed Jul. 1,1993, now abandoned, which is a continuation-in-part of U.S. applicationSer. No. 07/988,322, filed Dec. 9, 1992 now U.S. Pat. No. 5,372,138 byRobert J. Crowley et al., which is a continuation of U.S. applicationSer. No. 07/570,319, filed Aug. 21, 1990 by Robert J. Crowley et al. andnow abandoned, which is a continuation-in-part of U.S. application Ser.No. 07/171,039, now U.S. Pat. No. 4,951,677, filed Mar. 21, 1988 byRobert J. Crowley et al. The entire disclosures of U.S. Pat. No.4,951,677 and U.S. application Ser. No. 07/570,319 are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

The action of the human heart is controlled by propagation of electricalactivity in various regions of the heart. The presence of abnormalaccessory pathways in the heart can lead to conditions such asventricular tachycardia and atrial flutter. These conditions are verycommon. Approximately 20% of the population will have some type ofelectrical disturbance activity in the heart during their lifetimes.

Physicians have found that they can detect malfunctions of the heart byprobing the heart with a catheter fitted with one or more electrodes andhaving steering capability, measuring voltages within the heart, andobserving the waveforms. Once a physician understands how the electricalactivity of the heart is operating he can, if he wishes to do so, chooseto "disconnect" certain portions of the heart electrically by theprocess of ablation. If multiple electrode are used, the catheter canmake multiple readings simultaneously when it is curved inside theheart. Thus, the use of multiple electrodes shortens the time requiredto mad the heart.

The electrical activity of the heart is detected and read in accordancewith a mapping procedure to determine the presence of abnormal accessorypathways in the heart. A typical mapping procedure involves usingelectrophysiology sensing electrodes mounted on a catheter asremote-controlled voltage-testing probes to test various locations inthe heart.

The process of ablation is a destructive process in which the catheteris used to burn a certain section of the heart which stops thepropagation of an electrical signal from one portion of the heart toanother. Alternate means to perform ablation have been to inject achemical such as ethanol in specific regions of the heart, to apply verycold temperatures in a process called cryo-ablation, and to use sonicenergy, which is sometimes referred to as ultrasonic ablation. Theablation process may alternatively consist of applying low-frequency RFenergy to the heart tissue in order to create a burn. This burn willcause the tissue to heat up and desiccate and finally necrose.

Electrophysiology catheters are typically positioned at variouspositions in the heart under x-ray guidance. The x-rays show thecatheter, and can also show the heart itself and thus the position ofthe catheter relative to the heart if dye injections are made. Theclinician tries to visualize the position of the catheter in the heartin the various chambers. Electrical means are used to determine whetheror not the electrode is in contact with the heart, and this informationis shown on an EKG display. During the course of a typical procedure theoperator will frequently return to one or more positions, and will lookfor particular waveforms that he sees from the sensing electrodes todetermine whether the catheter has returned to the desired position.Typically, more than one catheter is used in a given procedure, and thecatheters are constructed with steering or torquing devices that assistin positioning of the catheters within the heart.

The sensing or ablation electrodes of intracardiac catheters aretypically made of tantalum, gold, or platinum. There can be as few asone or as many as five or more electrodes in a sensing and ablationcatheter. Typical sensing and ablation catheters will have at least onetip electrode and two, three, or four ring electrodes proximal to thetip electrode. The proximal ring electrodes are typically spaced fromthe distal tip in two, three, or four-millimeter increments. The ringelectrodes are generally bonded or crimped onto the catheter body orblended into the catheter body. The rings are sufficiently thick to haveenough mechanical strength when crimped to adhere to the catheter shaft.

It is known that the injections of chemicals such as ethanol into theheart can produce a response which is similar to that produced when aburn is made in the heart. Basically, the injection of chemicalsdisrupts or cuts off electrical pathways in the heart by causinglocalized cell death.

SUMMARY OF THE INVENTION

In one aspect, the invention features an acoustic imaging system for usewithin a body of a living being, having an elongated, flexible catheterconstructed to be inserted into the body, an ultrasound deviceincorporated into the elongated, flexible catheter, and an electrodemounted on a distal portion of the elongated, flexible catheter. Thereare a plurality of electrical conductors extending from a proximalportion of the elongated, flexible catheter to the distal portion. Atleast two of the plurality of electrical conductors are connected to theultrasound device and at least one of the plurality of electricalconductors is connected to the electrode. The ultrasound device isarranged to direct ultrasonic signals toward an internal structurewithin the body for the purpose of creating an ultrasonic image of theinternal structure, and the electrode is arranged for electrical contactwith the internal structure imaged by the ultrasound device.

The invention enables precise control and directability of cathetersused in electrophysiology procedures, with the aid of high resolutionimages that reveal the cardiac anatomy and the location of the catheterand electrodes relative to the various chambers of the heart, thevalves, the annuluses of the valves, and the other areas of the heart.Electrophysiology catheters according to the invention can be usedwithout x-ray guidance, thereby eliminating dye injections and prolongedexposure of the patient and clinician to x-rays during the procedure.The clinician need not rely on his own imagination when trying tovisualize the position of the catheter in the various chambers of theheart, and need not struggle to read an EKG display to determine whetheran electrode is in contact with heart tissue. Thus, the inventionreduces the time that it takes to obtain a reliable reading from aparticular region of the heart that can be identified with ultrasound.Moreover, the physician need not look for particular waveforms from asensing electrode to determine whether the electrode has returned to adesired position in the heart, and can reposition the electrode quicklyand precisely. Also, by reducing the time required for electrophysiologysensing procedures and enhancing the precision with which an electrodecan be positioned within the heart, the invention reduces the need forthe catheter to include a large number of electrodes in order to reducethe time required to map the heart.

If the electrode is used for ablation, the on-catheter imaging alsoensures that the electrode makes adequate contact with the endocardium,which is important because even if the catheter is in a position that isgood enough to record the cardiac electrical activity it may not be goodenough to deliver sufficient current to the portion of the heartrequiring the ablation. There is no need to look at the impedancebetween the electrode and the heart itself to determine whether theelectrode is in actual contact with the heart and there is nouncertainty as to whether the electrode is only in contact with blood,which of course is an electrical conductor and which would boil withoutcreation of a lesion at all.

The invention also enables monitoring of the ablation process once itbegins. The desiccation of tissue can be monitored by ultrasound, and itis useful to be able to see with ultrasound the depth and the extent ofthe lesion that is formed in the ablation procedure.

In another aspect, the invention features an acoustic imaging system foruse within a body of a living being, having an elongated, flexiblecatheter, an ultrasound device incorporated into the elongated, flexiblecatheter, and a chemical ablation device mounted on a distal portion ofthe elongated, flexible catheter. The ultrasound device is arranged todirect ultrasonic signals toward an internal structure within the bodyof the living being for the purpose of creating an ultrasonic image ofthe internal structure, and the chemical ablation device is arranged toablate at least a portion of the internal structure imaged by theultrasound device by delivery of fluid to the internal structure.

By providing a mode of ablation that does not require electrophysiologysensing electrodes to be used also as ablation electrodes, the inventionlowers the current delivery requirement for electrophysiology electrodesin electrophysiology catheters. I.e., an electrophysiology electrodeused solely for sensing need not be as good an electrical conductor asan electrophysiology electrode that is also used for ablation.

Another aspect of the invention features an acoustic imaging system foruse within a body of a living being, having an elongated, flexiblecatheter, an ultrasound device incorporated into the elongated, flexiblecatheter, and an ablation device comprising a transducer mounted on thedistal portion of the elongated, flexible catheter. The ultrasounddevice is arranged to direct ultrasonic signals toward an internalstructure within the body for the purpose of creating an ultrasonicimage of the internal structure. The transducer is constructed arrangedto convert electrical signals into radiation and to direct the radiationtoward the internal structure within the body for the purpose ofablating tissue. The ablation device is arranged to ablate at least aportion of the internal structure imaged by the ultrasound device.

Another aspect of the invention features a catheter system that includesan elongated, flexible catheter, an imaging system, a data collectionsystem, a central processing unit, and a graphic display system. Theimaging system is constructed and arranged to provide information fromwhich a graphical representation of an internal structure within thebody may be created. The data collection system is at least partiallylocated on a distal portion of the elongated, flexible catheter, and isconstructed and arranged to produce a plurality of items of datacorresponding to a respective plurality of locations within the internalstructure. The central processing unit is electrically connected to theimaging system and the data collection system, and is configured andarranged to create the graphical representation of the internalstructure from the information provided by the imaging system, and tosuper-impose onto the graphical representation the plurality of items ofdata provided by the data collection system. The plurality of items ofdata are super-imposed at locations on the graphical representation thatrepresent the respective plurality of locations within the internalstructure corresponding to the plurality of items of data. The graphicdisplay system is electrically connected to the central processing unit,and is constructed to display the graphical representation onto whichthe plurality of items of data are super-imposed.

By super-imposing items of data on a graphical representation of aninternal structure such as the heart, the invention provides an improvedway to display in a meaningful and readily understandable manner thesubstantial information that is stored and saved in connection with amapping procedure.

Another aspect of the invention features an acoustic imaging system foruse within a body of a living being, having an elongated, flexiblecatheter, an ultrasound device incorporated into the elongated, flexiblecatheter, and at least one sonolucent, electrically conductive structureincorporated into the elongated, flexible catheter. In one embodimentthe sonolucent structure is an electrode imprinted onto the cathetershaft as a thin film. The ultrasound device is arranged to directultrasonic signals through the sonolucent, electrically conductivestructure toward an internal structure within the body for the purposeof creating an ultrasonic image of the internal structure.

By eliminating the thickness of ordinary metal ring electrodes bonded orcrimped onto the body of a catheter, the invention enables an acousticimaging electrophysiology catheter (capable of sensing, ablation,steering, and imaging) to have a profile that is small enough to permiteasy access of several such catheters into the heart and to permit greatmaneuverability and flexibility of the catheters with minimal trauma tothe patient. In particular, the ultrasound imaging device occupiesconsiderable space in the assembly, and in order to make space for theultrasound imaging device the electrical wires can be placed on theperiphery of the catheter in accordance with the invention withoutadding substantially to the size of the catheter or interfering withimaging. The invention also allows an acoustic imaging electrophysiologycatheter to be sufficiently flexible, because very thin traces do notadd to the stiffness of the catheter in the way that individual wiressometimes do.

Another aspect of the invention features an ablation system for usewithin a body of a living being, having an elongated, flexible catheter,and an ablation device mounted on a distal portion of the elongated,flexible catheter, and a plurality of electrical conductors extendingfrom a proximal portion of the elongated, flexible catheter to thedistal portion. The ablation device includes a material that vibrates inresponse to electrical excitation, and the ablation device isconstructed and arranged to cause ablation of at least a portion of aninternal structure within the body. The ablation is at least assisted byvibration of the material.

Another aspect of the invention features a catheter system, having anelongated, flexible catheter, an acoustic imaging system constructed andarranged to direct ultrasonic signals toward an internal structurewithin the body for the purpose of creating an ultrasonic image of theinternal structure, and constructed and arranged to provide theultrasonic image, and an acoustic marker mounted on at least a distalportion of the elongated, flexible catheter. The acoustic marker isconstructed to emit a sonic wave when the acoustic marker iselectrically excited. The acoustic imaging system is constructed in amanner such that interference of the sonic wave emitted by the acousticmarker with the ultrasonic signals directed toward the internalstructure by the acoustic imaging system causes an identifiable artifactto appear on the ultrasonic image of the internal body structure.

Another aspect of the invention features a method of ablating hearttissue. An elongated, flexible catheter is provided that has anultrasound device and an ablation device incorporated into a distalportion thereof. The elongated, flexible catheter is inserted into abody of a living being, and the distal portion of the elongated,flexible catheter is introduced into the heart. The ultrasound device ispositioned in the vicinity of an internal structure within the heart,and ultrasonic signals are directed from the ultrasound device towardthe internal structure to create an ultrasonic image of the internalstructure. The internal structure is ablated through use of the ablationdevice mounted on the distal portion of the elongated, flexiblecatheter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a system showing use of an acousticcatheter.

FIG. 2 is a side view of a disposable catheter sheath for the acousticcatheter.

FIG. 3 is a longitudinal, partially cut away view of the distal end ofthe rotating assembly of the acoustic catheter.

FIG. 4 is a longitudinal, cross-sectional view of the distal end of theassembled acoustic catheter.

FIG. 5 is a longitudinal sectional view of the transducer element of thecatheter on a greatly magnified scale.

FIG. 6 is a diagrammatic representation of sound waves emanating fromthe acoustic lens of the catheter.

FIGS. 7-7d are longitudinal views of a catheter assembly illustratingsteps in filling the sheath and assembling the acoustic catheter, thesyringes shown in the figures being on a reduced scale.

FIG. 8 is a cross-sectional view of the motor-connector assembly towhich the catheter is connected, and FIG. 8a is a cross-sectional viewon an enlarged scale of a portion of FIG. 8.

FIGS. 9, 10 and 11 are graphical representations of torque in relationto angular deflection.

FIG. 12 is a block diagram of the electronic components useful with theacoustical catheter.

FIG. 13 is a longitudinal view of an acoustic imaging catheter sheathhaving electrodes for electrophysiology or cardiac ablation mounted onthe catheter sheath.

FIG. 14 is a block diagram of the principle components of an acousticimaging and electrophysiology system that includes the catheter shown inFIG. 13.

FIG. 15 is a partially cut-away view of a heart showing an acousticimaging and electrophysiology catheter being used to image a chamber ofthe heart.

FIG. 15a is a partially cut-away view of a heart showing an acousticimaging and electrophysiology catheter being used to image a portion ofa chamber of the heart that has been ablated by means of the electrodeson the catheter sheath.

FIG. 16 is a longitudinal view of an acoustic imaging catheter sheathwhich is deflectable by actuation from the proximal end, and whichincludes electrodes for electrophysiology or ablation mounted on thecatheter sheath.

FIG. 17 is a longitudinal cross-sectional view of an acoustic imagingcatheter sheath having a sonolucent metallic electrode and having asonolucent metallic trace leading to the electrode.

FIG. 18 is a longitudinal cross-sectional view of an acoustic imagingcatheter sheath having a sonolucent metallic electrode and having aprotective covering over the electrode with micro-apertures drilledthrough the covering.

FIG. 18a is a longitudinal cross-sectional view of the acoustic imagingcatheter sheath of FIG. 18 showing the micro-apertures filled withconductive material.

FIG. 19 is a longitudinal view of a catheter sheath having a balloon incombination with an electrode for electrophysiology or cardiac ablation,and FIGS. 19a, 19b and 19c are longitudinal views of the distal portionof the catheter sheath shown in FIG. 19, illustrating stages ofinflation of the balloon.

FIG. 20 is a partially cut-away longitudinal view of a catheter sheathhaving a balloon on which a set of electrodes is coated, the balloonbeing constructed of electrically excitable material and having a set ofperfusion ports in its wall.

FIG. 21 is a partially cut-away longitudinal view of a catheter sheathhaving a balloon through which a fluid-injection needle passes, theballoon being constructed of electrically excitable material and havinga set of perfusion ports in its wall.

FIG. 21a is an enlarged view, partially in cross-section of thefluid-injection needle shown in FIG. 21 exiting through a wall of theballoon.

FIG. 22 is a longitudinal view of one embodiment of an acoustic imagingballoon catheter.

FIG. 23 is an expanded longitudinal cross-sectional view of the proximalend of the catheter coupling of the acoustic imaging balloon catheter ofFIG. 22, in partial cross-section.

FIGS. 24, 25, and 26 are longitudinal views of alternative embodimentsof acoustic imaging balloon catheters enabling relative axialpositioning of the transducer and the balloon.

FIG. 27 is a longitudinal view of an acoustic imaging catheter sheathhaving a hollow needle, extending from the distal tip of the cathetersheath, for injection of fluid into cardiac tissue, and FIG. 27a is adetailed cross-sectional view of the distal tip of the catheter sheathshown in FIG. 27.

FIG. 28 is a longitudinal view of an acoustic imaging catheter sheathhaving a needle, extending from the distal tip of the catheter sheath,constructed of an electrically excitable material that generatesacoustic energy when excited, and FIG. 28a is a detailed, partiallycross-sectional view of the distal tip of the catheter sheath shown inFIG. 28.

FIG. 29 is a perspective view of an acoustic imaging catheter sheathhaving a hollow needle, extending from a side wall of the cathetersheath, for injection of fluid into cardiac tissue, and havingelectrodes for electrophysiology or cardiac ablation mounted on thecatheter sheath, and FIG. 29a is a detailed, partially cross-sectionalview of the distal tip of the catheter sheath shown in FIG. 29.

FIG. 30 is a longitudinal view of an acoustic imaging catheter sheathhaving a wire in the shape of a cork screw attached to its distal end,and FIG. 30a is a detailed, partially cross-sectional view of the distaltip of the catheter sheath shown in FIG. 30.

FIG. 31 is a longitudinal view of an acoustic imaging catheter sheathhaving a wire in the shape of a cork screw passing through its distalend, the wire being attached to the drive shaft within the sheath, andFIG. 31a is a detailed, partially cross-sectional view of the distal tipof the catheter sheath shown in FIG. 31.

FIG. 32 is a longitudinal view of an acoustic imaging catheter sheathenclosing a drive shaft on which an imaging transducer and an ablationtransducer are mounted, and FIG. 32a is a detailed, partiallycross-sectional view of the distal tip of the catheter sheath shown inFIG. 32.

FIG. 33 is a partially cut-away view of a heart and a portion of anesophagus, showing the use of a trans-esophageal probe in combinationwith two catheters whose distal portions are located within a heartchamber.

FIG. 34 is a block diagram of the principle components of an acousticimaging and electrophysiology system that includes an electrophysiologycatheter and a display that super-imposes electrophysiology data on animage of the heart.

FIG. 35 is a cross-sectional view of a catheter having a rotatable driveshaft on which a mirror is mounted, the mirror being configured toreflect ultrasound signals produced by a transducer.

DETAILED DESCRIPTION

General Structure

Referring to FIG. 1, a micro-acoustic imaging catheter 6 according tothe invention is driven and monitored by a control system 8. Thecatheter is comprised of a disposable catheter sheath 12 (FIGS. 2 and 4)having a sound-transparent distal window 24 provided by dome element 25(FIG. 4), in which is disposed a miniature, rotatable ultrasonictransducer 10 (FIGS. 3 and 4) driven by a special, high fidelityflexible drive shaft 18. A relatively rigid connector 11 is joined tothe proximal end of the main body of the catheter sheath, adapted to bejoined to a mating connector of drive and control system 8.

The catheter is adapted to be positioned within the heart by standardcatheter procedures by guiding the flexible catheter through variousblood vessels along a circuitous path, starting, for example, bypercutaneous introduction through an introducer sheath 13 disposed in aperforation of the femoral artery 15.

Referring to FIG. 2, disposable catheter sheath 12 is a long tube,extruded from standard catheter materials, here nylon, e.g. with outerdiameter, D, of 2 mm, wall thickness of 0.25 mm and length of 1 meter.Dome element 25, connected to the distal end of the tube, is asemi-spherically-ended cylindrical transducer cover constructed ofmaterial which is transparent to sound waves, here high impactpolystyrene. This dome element has a thickness of approximately 0.125 mmand a length E of about 8 mm. For purposes described later herein,catheter sheath 12 in its distal region preferably tapers down overregion R as shown in FIG. 4 to a narrowed diameter D' at its distal end,achieved by controlled heating and drawing of this portion of theoriginal tube from which the sheath is formed. Catheter sheath 12 andacoustically transparent dome element 25 are adhesively bonded together.

Referring to FIGS. 3 and 4, the drive shaft assembly 18 is formed of apair of closely wound multi-filar coils 26, 28 wound in opposite helicaldirections. These coils are each formed of four circular cross-sectionalwires, one of which, 30, is shown by shading. Coils 26, 28 are solderedtogether at both the distal and proximal ends of the assembly ininterference contact, here under rotational pre-stress. By alsoproviding a pitch angle of greater than about 20°, a substantial part ofthe stress applied to the wire filaments of the coil is compression ortension in the direction of the axis of the filaments, with attendantreduction of bending tendencies that can affect fidelity of movement.There is also provision to apply a torsional load to the distal end ofthe assembly to cause the drive shaft to operate in the torsionallystiff region of its torsional spring constant curve, achieved by viscousdrag applied to the rotating assembly by liquid filling the narroweddistal end of the catheter sheath (FIG. 4). Such loading, together withinitial tight association of the closely wound filaments in theconcentric coils, provides the assembly with a particularly hightorsional spring constant when twisted in a predetermined direction.Thus, despite its lateral flexibility, needed for negotiating tortuouspassages, the assembly provides such a torsionally stiff and accuratedrive shaft that rotary position information for the distal end can,with considerable accuracy, be derived from measurement at the proximalend of the drive shaft, enabling high quality real-time images to beproduced. Further description of the coils of the drive shaft and theircondition of operation is provided below.

Coaxial cable 32 within coils 26, 28 has low power loss and comprises anouter insulator layer 34, a braided shield 36, a second insulator layer38, and a center conductor 40. Shield 36 and center conductor 40 areelectrically connected by wires 42, 44 (FIG. 5) to piezoelectric crystal46 and electrically conductive, acoustical backing 48 respectively, ofthe transducer. Helical coils 26, 28, especially when covered with ahighly conductive metal layer, act as an additional electric shieldaround cable 32.

Transducer crystal 46 is formed in known manner of one of a family ofceramic materials, such as barium titanates, lead zirconate titanates,lead metaniobates, and PVDFs, that is capable of transforming pressuredistortions on its surface to electrical voltages and vice versa.Transducer assembly 10 is further provided with an acoustic lens 52. Theradius of curvature B of lens surface 52 is greater than about 2.5 mm,chosen to provide focus over the range f (FIG. 6) between about 2 to 7mm. The lens is positioned at an acute angle to the longitudinal axis ofthe catheter so that, during rotation, it scans a conical surface fromthe transducing tip, the angle preferably being between 10° and 80°,e.g., 30°. Transducer backing 48 is acoustically matched to thetransducer element to improve axial resolution.

The transducer assembly 10 is supported at the distal end of the driveshaft by a tubular sleeve 29 which is telescopically received over adistal extension of the inner coil 28, as shown in FIG. 3.

Referring again to FIG. 4, the length, E, of dome element 25 issufficient to provide headroom F for longitudinal movement of transducer10 within the dome element as catheter sheath 12 and coils 26, 28 aretwisted along the blood vessels of the body. In the untwisted state,transducer 10 is a distance F, about 2 to 3 mm, from the internal endsurface of the dome element 25. The dome element, along with cathetersheath 12 is adapted to be filled with lubricating andsound-transmitting fluid.

FIGS. 7-7b show the filling procedure used to prepare ultrasoundcatheter sheath 12 (or any of the other interchangeable sheathsdescribed below) for attachment to the ultrasound imaging drive shaftand transducer assembly. A sterile, flexible filling tube 17 attached toa syringe 19 is filled with sterile water. This filling catheter isinserted into the ultrasound catheter sheath 12, all the way to thedistal tip. The water is then injected until it completely fills and theexcess spills out of the ultrasound catheter while held in a verticalposition, see FIG. 7a. This expels air from the catheter which couldimpair good acoustic imaging. Continued pressure on the plunger of thesyringe causes the flexible tube 17 to be pushed upward, out of catheter12, FIG. 7b, leaving no air gaps behind. This eliminates the necessityto carefully withdraw the flexible filling tube at a controlled ratewhich could be subject to error. A holding bracket 21 is used to holdthe catheter vertical during this procedure.

After the catheter sheath 12 is filled, the acoustic transducer 10 andshaft 18 are inserted, displacing water from the sheath 12, until theinstalled position, FIG. 7d, is achieved.

FIGS. 8 and 8a (and FIG. 1, diagrammatically) show the interconnectionarrangement for a connector 7 at proximal end of the acoustic catheterwith connector 16 of the driving motor 20, and the path of the electricwires through the center shaft 43 of the driving motor. The center shaftand connector 16 rotate together, as do the wires that pass through thehollow motor shaft. The latter connect to a rotating electrical joint27, which is held stationary at the back end and is connected tostationary coaxial cable 45 through a suitable connector such as acommon BNC type. The enlarged view shows how the motor connector 16 andthe driveshaft connector 7 mate when the two assemblies are pushedtogether, thereby making both electrical and mechanical contact. Thecatheter connector 7 is held in position by an ordinary ball bearingwhich provides a thrusting surface for the rotating connector 16 anddriveshaft 18 while allowing free rotation. The disposable cathetersheath 12 includes an inexpensive, relatively rigid hollow bushing 11 ofcylindrical construction that allows it to be slid into and held bymeans of a set screw in the housing that captures the non-disposablebearing, connector and driveshaft 18. The longitudinal and rotationalposition of hollow bushing 11 relative to the housing is adjustable.Drive shaft coil assembly 18, thus attached at its proximal end toconnector 16 of drive motor 20, rotates transducer 10 at speeds of about1800 rpm. The transducer 10 is electrically connected by coaxial cable32 extending through coil assembly 18 and via the cable through themotor to the proximal electronic components 22 which send, receive andinterpret signals from the transducer. Components 22 include a cathoderay tube 23, electronic controls for the rotary repetition rate, andstandard ultrasonic imaging equipment; see FIG. 12. A rotation detector,in the form of a shaft encoder shown diagrammatically at 19, detects theinstantaneous rotational position of this proximal rotating assembly andapplies that positional information to components 22, e.g., for use inproducing the scan image.

Because the rotation detector depends upon the position of proximalcomponents to represent the instantaneous rotational position of thedistal components, the rotational fidelity of the drive shaft is ofgreat importance to this embodiment.

Manufacture and Assembly of the Drive Shaft

Referring to FIGS. 3 and 4, coils 26, 28 are each manufactured bywinding four round cross-section stainless steel wires of size about 0.2mm, so that D_(o) is about 1.3 mm, D_(i) is about 0.9 mm, d_(o) is about0.9 mm and d_(i) is about 0.5 mm. The coils are closely wound with apitch angle α_(o) and α_(i) where α_(o) is smaller than α_(i), e.g.,221/2° and 31°, respectively. Flat wires having a cross-sectional depthof about 0.1 mm may also be used. The pitch angles are chosen toeliminate clearances 60 between the wires and to apply a substantialpart of the stress in either tension or compression along the axis ofthe wire filaments. The coils, connected at their ends, are adapted tobe turned in the direction tending to make outer coil 26 smaller indiameter, and inner coil 28 larger. Thus the two assemblies interferewith each other and the torsional stiffness constant in this rotationaldirection is significantly increased (by a factor of about 6) due to theinterference. Operation of the driveshaft in the torsionally stiffregion with enhanced fidelity is found to be obtainable by adding atorsional load to the distal end of the rotating assembly of thecatheter. The importance of rotational fidelity and details of how it isachieved warrant further discussion.

For ultrasound imaging systems, the relative position of the ultrasoundtransducer must be accurately known at all times so that the returnsignal can be plotted properly on the display. Any inaccuracy inposition information will contribute to image distortion and reducedimage quality. Because position information is not measured at thedistal tip of the catheter, but rather from the drive shaft at theproximal end, only with a torsionally stiff and true drive shaft canaccurate position information and display be obtained.

Furthermore, it is recognized that any drive shaft within a cathetersheath will have a particular angular position which is naturallypreferred as a result of small asymmetries. Due to this favoredposition, the shaft tends, during a revolution, to store and thenrelease rotational energy, causing non uniform rotational velocity. Thisphenomenon is referred to as "mechanical noise" and its effect isreferred to as "resultant angular infidelity" for the balance of thisexplanation.

According to the present invention, use is made of the fact thatsuitably designed concentric coils interfere with each other, as hasbeen mentioned previously. When twisted in one direction, the outerlayer will tend to expand and the inner layer contract thus resulting ina torsional spring constant which is equal only to the sum of the springconstants of each of the two shafts. When, however, twisted in theopposite direction, the outer layer will tend to contract while theinner layer will expand. When interference occurs between the inner andouter layers the assembly will no longer allow the outer coil tocontract or the inner to expand. At this point, the torsional springconstant is enhanced by the interference between the shafts and thetorsional spring constant is found to become five or ten times greaterthan the spring constant in the "non-interference" mode.

Referring to FIG. 9, the relationship between torque and angulardeflection for such a coil assembly is shown, assuming one end fixed andtorque applied at the opposite end. `Y` represents mechanical noise; `Z`resultant angular infidelity; `T` the interference point; the slope ofthe line `U`, the torsional spring constant (TSC) without interference(i.e., the sum of the torsional spring constant of each of the twocoils); and the slope of the line `V`, the TSC with interference. Thus,TSC is shown to increase dramatically at the interference point.

Referring to FIG. 10, by pre-twisting the shafts relative to one anotherand locking their ends together in a pre-loaded assembly, theinterference point is moved to be close to the rest angle and resultantangular infidelity, Z, is reduced in the given direction of rotation.

To improve upon this effect even further, dynamic frictional drag isintentionally introduced at the distal end of the shaft to raise thelevel of torque being continually applied to the system. This ensuresoperation of the shaft in the region of the high torsional springconstant or "interference" mode throughout its length, producing arotationally stiffer shaft. This is shown in FIG. 11, where `W` isdynamic load and `X` is the region of operation. The use of such dynamicdrag is of particular importance in certain catheters of small diameter,e.g. with outer diameter less than about 2 mm.

To form inner coil 28, four individual wires are simultaneously woundaround a mandrel of about 0.5 mm outer diameter. The free ends of thiscoil are fixed, and then four wires are wound in opposite hand directlyover this coil to form the outer coil 26. The wires are wound undermoderate tension, of about 22.5 gm/wire. After winding, the coils arereleased. The inner mandrel, which may be tapered or stepped, or have aconstant cross-sectional diameter, is then removed. The wire ends arefinished by grinding. One end is then soldered or epoxied to fix thecoils together for a distance of less than 3 mm. This end is held in arigid support and the coils are then twisted sufficiently, e.g. 1/4turn, to cause the outer coil to compress and the inner coil to expand,causing the coils to interfere. The free ends are then also fixed.

The coil assembly 18 is generally formed from wires which provide a lowspring index, that is, the radius of the outer coil 26 must be not morethan about 2.5 to 10 times the diameter of the wires used in itsconstruction. With a higher index, the inner coil may collapse. Themulti-filar nature of the coils enables a smaller diameter coil to beemployed, which is of particular importance for vascular catheters andother catheters where small size is important.

After the coil assembly is completed, coaxial cable 32 is insertedwithin the inner coil. The cable may be silver-coated on braid 36 toenhance electrical transmission properties. It is also possible to usethe inner and outer coils 26, 28 as one of the electrical conductors ofthis cable, e.g. by silver coating the coils.

Referring back to FIGS. 3 and 5, to form transducer 10, wire 42 issoldered to either side of electrically conducting sleeve 29 formed ofstainless steel. Wire 44 is inserted into a sound absorbent backing 48which is insulated from sleeve 29 by insulator 72. Piezoelectric element46 of thickness about 0.1 mm is fixed to backing 48 by adhesive andelectrical connection 74 is provided between its surface and the end ofsleeve 29. Thus, wire 42 is electrically connected to the outer face ofpiezoelectric element 46, and wire 44 electrically connected to itsinner face. Spherical lens 52, formed of acoustic lens materials isfixed to the outer surface of element 46.

Referring to FIGS. 4 and 7-7d, the completed drive shaft 18 andtransducer 10 are inserted into disposable catheter sheath 12,positioning transducer 10 within acoustically transparent dome element25, with liquid filling the internal open spaces. The catheter thusprepared is ready to be driven by the drive assembly; see FIG. 8.

During use, rotation of drive shaft 18, due to exposure of the helicalsurface of the outer coil to the liquid, tends to create helicalmovement of the liquid toward the distal end of the sheath. This tendsto create positive pressure in dome element 25 which reduces thetendency to form bubbles caused by out-gassing from the various surfacesin this region.

As has been mentioned, it is beneficial to provide added drag frictionat the distal end of the rotating drive shaft 18 to ensure operation inthe torsionally stiff region of the torsional spring constant curve. Itis found that this may be done by simply necking down the distal portionof the catheter sheath 12, as shown in FIG. 4 to provide a relativelytight clearance between the distal portion of the shaft 18 and the innersurface of the sheath, to impose the desired degree of viscous drag. Asan alternative, the dynamic drag may be provided by an internalprotrusion in catheter sheath 12 to create a slight internal frictionagainst drive shaft 18.

The acoustic catheter may be constructed so that it may be preformedprior to use by standard methods. Thus, if the investigator wishes topass the catheter through a known tortuous path, e.g., around the aorticarch, the catheter can be appropriately shaped prior to insertion. Suchpreformation can include bends of about 1 cm radius and still permitsatisfactory operation of the drive shaft.

Electronics

FIG. 12 is a block diagram of the electronics of a basic analogultrasound imaging system used with the acoustical catheter. The motorcontroller (D) positions the transducer B for the next scan line. Thetransmit pulsed (A) drives the ultrasound transducer. The transducer (B)converts the electrical energy into acoustic energy and emits a soundwave. The sound wave reflects off various interfaces in the region ofinterest and a portion returns to the transducer. The transducerconverts the acoustic energy back into electrical energy. The receiver(C) takes this wave-form and gates out the transmit pulse. The remaininginformation is processed so that signal amplitude is converted tointensity and time from the transmit pulse is translated to distance.This brightness and distance information is fed into a vectorgenerator/scan converter (E) which along with the position informationfrom the motor controller converts the polar coordinates to rectangularcoordinates for a standard raster monitor (F). This process is repeatedmany thousands of times per second.

By rotating the transducer at 1800 rpm, repeated sonic sweeps of thearea around the transducer are made at repetition rate suitable for TVdisplay, with plotting based upon the rotary positional informationderived from the proximal end of the device. In this way a real timeultrasound image of a vessel or other structure can be observed.

Due to its rotational fidelity, the device provides a relatively highquality, real time image of heart tissue. It is also possible to form3-dimensional images using appropriate computer software and by movingthe catheter within the heart.

Selectable Catheter Sheaths

A wide variety of novel disposable catheter sheaths can be substitutedfor catheter sheath 12 and used in the system.

FIG. 13 shows a flexible, disposable catheter sheath 12c on which aremounted a plurality of electrophysiology or ablation electrodes 300.Catheter sheath 12c may be combined with any of the technologiesdescribed below in connection with FIGS. 24, 25, and 26 to permitrelative longitudinal movement between the transducer and electrodes300.

With reference to FIG. 14, an ultrasound/electrophysiology catheter 392such as the one shown in FIG. 13 is connected to an ultrasound imagingsystem 338 that receives signals from the ultrasound transducer andtransmits image data to display system 390 for display as an ultrasoundimage. RF generator 340 generates RF electrical signals for excitationof the ultrasound transducer or the electrodes. By observing in realtime, on display system 390, the region of the heart nearultrasound/electrophysiology catheter 392, a physician can determine theposition of the catheter sheath and electrodes relative to cardiactissue and can also reposition catheter 392 at the same location at alater time. In order to reposition the catheter at the same location thephysician either remembers the image or "captures" and stores the imageusing videotape or computer storage capabilities, so that the physiciancan compare the real time image with the captured or remembered image todetermine whether the catheter has returned to the desired location.

One of the questions that arises during the course of positioning thecatheter is whether or not a particular electrode is really in goodelectrical contact with the cardiac tissue. By visualizing the positionof the electrode relative to the endocardium, the physician can make ajudgment whether that electrode is in the proper position for a reliablereading. If not, the catheter can be readily repositioned by twistingthe catheter and manipulating a steering wire, such as the one describedin connection with FIG. 16 below, until the electrode or electrodes arein position. Without the use of visual information, the physician couldcontinue to reposition the catheter in many locations of the heart andcould compare these readings until he gets a picture in his mind of whatthe overall electrical activity of the heart is like. Using visualinformation, however, the physician can develop a better strategy thatwill tell him what areas of the heart he may ablate (using any of avariety of ablation techniques) in order to correct any perceiveddeficiencies in the electrical activity of the heart. FIGS. 15 and 15ashow an acoustic imaging and electrophysiology catheter 348 being usedto image a chamber of heart 350 before and after ablation of hearttissue, respectively.

Because the ultrasound transducer is being used to image points ofactual contact of the surface of the electrode with cardiac tissue, itis necessary for the transducer to have close-up imaging capability,i.e., the ability to image from essentially the surface of the catheteroutward. This close-up imaging capability is accomplished by using avery high frequency, such as 20 megahertz or higher. In certaincircumstances, in which a compromise between close-up imaging and depthof penetration is desired, lower frequencies such as 10 megahertz couldbe used (there tends to be a trade-off between close-up and depth ofpenetration).

It is also possible to have more than one transducer on the same rotaryshaft, one transducer being used for close-up imaging and the otherbeing used for depth of penetration. Alternatively, there may be asingle, multifrequency transducer, which is a step transducer having apiezo-electric element that has a series of concentric plates or zonesof varying thicknesses. In one embodiment there would be two zones: acentral zone that occupies half of the surface area of the transducerand that has thickness appropriate for generating acoustic waves in theorder of 30 megahertz, and an annular zone around the central zone thathas a greater thickness appropriate for generating acoustic waves around10 megahertz. It is advantageous to have a single, multifrequencytransducer rather than two different transducers because if a single,multifrequency transducer is used the user can select at will the depthof penetration desired and the frequency of operation desired withouthaving to shift the position of the catheter, whereas if two transducersare used it may be necessary to shift the position of the catheterunless the two transducers oppose each other on opposite sides of thedrive shaft.

The electrophysiological information obtained from electrodes 300 can beused to determine the location of catheter sheath 12c within the heart,as an alternative to using the ultrasound transducer. In particular,there are certain voltage patterns that are obtained during theelectrophysiology procedure that identify certain landmarks in theheart.

If electrodes 300 are used for ablation, the imaging capability of thecatheter can be used to determine immediately whether a specific changeto the tissue has resulted from the ablation. Desiccation of tissuemanifests itself as a brightening of the region of the ultrasound imagecorresponding to the location of the lesion. This brighteningcorresponds to increased reflection of ultrasonic signals.

FIG. 16 shows sheath 12f on which are mounted electrodes 300 forelectrophysiology or ablation. Sheath 12f has a two lumen construction.The large lumen contains the transducer and drive shaft while the smalllumen contains a wire 94. As shown, wire 94 is a deflecting or steeringwire attached near the distal end, and is free to slide through itslumen under tension applied to ring 96 to cause the catheter to bendwhen pulled taut, thus providing a measure of control of the orientationof the distal end of the acoustic catheter while negotiating thepassages of the body or the like. In another embodiment wire 94 may be apreformed stylet, which, when inserted through the second lumen, causesdeflection of the tip.

FIG. 17 shows an acoustic imaging catheter sheath 302 having asonolucent metallic electrode 304 for sensing electrical potentials orfor ablation, and having a pair of sonolucent metallic traces 306leading to electrode 304. Catheter sheath 302 has a diameter of ninefrench or less, and most preferably six french or less. Imagingtransducer 308, because it is slidable (in accordance with any of thetechniques described below in connection with FIGS. 24, 25, and 26), canbe placed under or near electrode 304.

Because metal electrodes are very efficient reflectors of ultrasoundenergy, one would expect that there would be a high likelihood thatreverberation artifacts would result when trying to image directly near,or as close as possible to, electrode 304 itself. Nevertheless, asdescribed below, it is possible to make the electrode acousticallytransparent, so that such reverberation artifacts do not tend to result,while the electrode is sufficiently conductive to perform the task ofsensing and has a sufficiently low resistance to perform the function ofablation. The resistance from the proximal connector of the catheter toelectrode 304 should be no more than 50 to 100 ohms for sensing and nomore than 25 to 50 ohms for ablation. Otherwise, undue heating of thecatheter could occur.

In one method of fabricating catheter sheath 302, a sonolucent tube ofpolyethylene is imprinted with conductive material to form electrode 304and traces 306 leading to electrode 304. Electrode 304 and conductivetraces 306 are made of aluminum that is deposited by vacuum deposition,which has been found to produce a low resistance, high reliability,conductive path that is sufficiently thin to allow ultrasound energy topass through the aluminum almost unhindered. Then a covering 310, whichis also sonolucent, is applied over the conductively treated catheterbody to protect and seal electrode 304 and traces 306. Covering 310includes micro-apertures filled with conductive material, as shown inFIG. 18a below. Because catheter sheath 302 and covering 310 are formedof a sonolucent material and because electrode 304 and traces 306 do nottend to reflect ultrasound energy, the presence of electrode 304 andtraces 306 does not tend to create artifacts in the ultrasound image.

We now describe the vacuum deposition technique by which electrode 304and traces 306 are deposited onto the sonolucent tube. First, thesonolucent tube, which is a single-lumen extrusion, is placed on amandrel in a manner such that it can be held straight. Then a flatcopper plate, such as is used for lithography, is photoetched over anarea as long as the sonolucent tube and as wide as the circumference ofthe sonolucent tube in a manner such that a negative of the pattern ofthe traces and the electrode is imprinted upon the plate. The pattern isin the form of a waxy ink material rolled onto the copper plate. Thesonolucent tube is than placed onto the copper plate at one side androlled to the other side, which causes the sonolucent tube to be printedaround its entire periphery in the manner of a printing roll.

The sonolucent tube is then placed into a chamber that is evacuated,with the mandrels being placed on a rotisserie so that they rotate. Thesonolucent tube is coated with metal by a vacuum deposition process inwhich the metal is caused to melt in a graphite boat by inductionheating and then the metal evaporates and deposits over the entiresurface of the sonolucent tube. The metal covers both the areas wherethe ink is located and the areas where there is no ink. Then thesonolucent tube is removed from the chamber and is washed with a solventsuch as trichlorethylene. This process washes away the ink with thealuminization that covers the ink, leaving the areas that are notprinted with the ink intact with a thin aluminum coating.

The metal may alternatively be deposited onto the sonolucent tube bylaser xerography, according to which a charge is put on the surface ofthe sonolucent tube, which tends to selectively accept aluminum ions orcharged molecules as they are deposited. The metal is deposited by avacuum deposition process in which the metal is caused to melt in a boaton which a charge has been placed, and the metal evaporates and chargedmetal particles deposit in the appropriate places on the sonolucent tubein accordance with xerographic techniques.

Alternative methods of depositing the metal onto the sonolucent tubeinclude spraying a conductive paint onto a pattern on the sonolucenttube or spraying with a plasma gun (a small electron gun) that iscapable of selectively depositing evaporated metal in specific areas onthe sonolucent tube. The gun doesn't actually touch the surface of thesonolucent tube, but sprays the surface in a manner analogous to a verytiny airbrush.

If multiple electrode rings are formed on the sonolucent tube, some ofthe electrode rings may not completely encircle the sonolucent tubebecause certain traces would have to pass through these electrode rings.Alternatively, the traces and protective sonolucent coverings could bedeposited as a multi-layer structure. For example, an electrode near thetip of the sonolucent tube could be deposited as a complete ringconnected to a trace extending along the length of the sonolucent tube,and then a protective sonolucent covering could be placed over thedeposited metal, and then a second deposition process could be performedto lay down a second ring, and so on as various layers of material arebuilt up one on top of the other.

Another method of fabricating the catheter is to first print electrode304 and traces 306 on a flat sheet of acoustically transparent materialsuch as polyimide, and to roll that sheet up in a spiral like ajelly-roll and either place the sheet on the sonolucent tube or have thesheet be the sonolucent tube itself.

To prevent damage to the fragile electrodes and traces, a thin,acoustically transparent covering is placed over the aluminized ormetallized catheter body. The covering may be nylon that is expanded andthen shrunk onto the catheter body, or polyethylene that is shrunk ontothe catheter body. Alternatively, the covering may be formed by sprayingor dipping methods. Nylon and polyethylene are dialectic materials, andthus function as electrical insulators that would prevent the electrodesfunctioning when placed in proximity to the heart tissue were it not forthe fact that microapertures are drilled through the protective coating.

As shown in FIGS. 18 and 18a, the microapertures 330 in a protectivecoating 332 over a sonolucent electrode 334 and a sonolucent substrate366 are very small holes, e.g., one micron in diameter or up to tenmicrons in diameter, drilled by UV eximer laser machining techniques,and are as thick as protective coating 332. The number of pulses of theeximer laser is selected in a manner such that the laser penetrates thethickness of the coating but does not to go below metal electrode 334;in any event, when the laser hits the metal it is just reflected anyway.The eximer laser technology could be provided by Resonetics, Nashua,N.H. 03063.

The density of microapertures 330 is as high as possible consistent withthe strength of the materials. Generally, one needs to have 62,500apertures in an area that is 3 square millimeters. The apertures can beformed very rapidly by indexing and also by optical steering while thecatheter body is rotating. After these apertures are formed, theapertures are filled with a conductive jell material 336 such as thatused for EKG electrodes at the place of manufacture of the cathetersheath. The conductive jell is then wiped clear of the catheter sheath.Alternatively, the apertures can be filled with an epoxy that includestantalum, gold powder, or silver powder, or PVDF filled with a metalpowder.

If the electrode is to be used for high-current ablation, theelectrode-to-terminal resistance should be no more than 20 to 50 ohms,rather than the limit of 50 to 100 ohms that is acceptable for sensingpurposes. The better conduction required for ablation can be achieved byapplying additional gold plating over the areas that have been drilledwith the micro-apertures, using masking and plating techniques or vacuumdeposition, or using a gold plating solution.

An alternative to using the micro-apertures is to have the aluminizedsurfaces of the electrode simply exposed and to put protective coveringover the traces but not the electrode. In order to minimize problems dueto wear and handling of the electrodes, the exposed electrodes should besubjected to proper surface treatment and texturing.

FIGS. 19-19c show a catheter sheath 12d on which is mounted a balloon 55very near the tip of catheter sheath 12d. The balloon is adapted to bepressurized with liquid, such as saline or water, or a gas, such as air,through the same lumen that holds the ultrasound imaging device, via aninflation opening in the wall of the catheter sheath. The balloon may beused to center or position the ultrasound device securely within a heartchamber and maintain its position away from an area of interest on awall of the heart. The balloon in its collapsed or unpressurized stateis easily inserted prior to positioning and may be accurately positionedby use of ultrasound imaging during initial placement. In otherembodiments a separate lumen is provided for inflation of the balloonand/or the balloon is spaced from the distal end of the catheter.

If balloon 55 is filled with air at an appropriate point in time theballoon floats in a manner that assists the positioning of the catheter.For example, the balloon might float upwards from a lower ventricle to ahigher atrium, for instance. The balloon physically moves the tip of thecatheter from one location in the heart to another in a manner which isnot possible with steering and pushing, although the balloon can be usedin conjunction with such steering and pushing techniques. For example,the embodiment shown in FIG. 19 may be modified to include the steeringwire shown in FIG. 16.

If balloon 55 is filled with air it can move either with the flow ofblood or against the flow. If the balloon is inflated with liquid, suchas saline, it becomes a flow-directed balloon that can travel only withthe flow of blood. Such a flow-directed balloon is also useful to directthe catheter in the heart. Cardiologists know the path of flow in theheart very well, and if a cardiologist knows that the direction of flowin the heart is favorable for use of a flow-directed balloon, he canfill the balloon with fluid to cause it to move with the flow.

Thus, the air-filled or fluid-filled balloon simplifies the task ofpositioning the catheter, even if the catheter includes steering ortorquing devices that assist in positioning of the catheter within theheart. Balloon 55 can also be used to perform other functions in theheart, such as valvularplasty.

In one embodiment balloon 55 is acoustically transparent, so that itdoesn't obstruct the field of view of the acoustic imaging transducer.Materials such as cross-link polyethylene have high inflation strength,good biocompatability, processability, freedom of pinholes, and very lowacoustic attenuation. These are commonly used balloon materials. It isalso possible to use a latex or silicone balloon.

Frequently, when performing an electrophysiology sensing procedure or anelectrode ablation procedure the clinician would like to apply pressureto the electrode and its adjacent heart tissue in order to assure a firmcontact. Accordingly, in one embodiment, balloon 55 is an "opposingpositioning balloon," i.e., a balloon that engages a wall of the heartor a structure such as the coronary sinus when the balloon is inflatedin such a way as to cause one or more electrodes to press firmly againstthe cardiac tissue. FIG. 19 shows a single sensing or ablation electrode394 mounted on the distal end of catheter sheath 12d, but in alternativeembodiments there is more than one electrode. The electrode orelectrodes may be mounted on catheter sheath 12d (as in FIG. 19), or onballoon 55 (as in FIG. 20), or on both catheter shaft 12d and balloon55. With reference to FIG. 20, electrodes 394 can be printed on orplaced on balloon 55 as rings or stripes by vacuum deposition, in amanner analogous to the method, described above, of creatingacoustically transparent electrodes on a catheter sheath. Electrodes oncatheter sheath 12d can also be created by this method, or can be simplemetal rings of gold, silver, tantalum etc. FIG. 19 shows opposingpositioning balloon 55 concentric to catheter sheath 12d, but in otherembodiments the opposing positioning balloon is eccentric to thecatheter sheath and the balloon is used to press the side of thecatheter sheath itself the heart wall.

FIG. 21 shows balloon 55 combined with a chemical ablating needle 396,such as the one described below in connection with FIGS. 27 and 27a,that is constructed to inject a chemical into heart tissue to ablate thetissue. Needle 396 exits through a side wall of balloon 55, as shown indetail in FIG. 21a. Alternatively, needle 396 may exit catheter sheath12d near balloon 55. Balloon 55 is made of an electrically excitable,acoustic generating material such as polyvinylidene fluoride (PVDF).During use, needle 396 is inserted into tissue under ultrasoundguidance, the balloon is inflated, and the balloon material iselectrically excited to aid the transfer of fluid from the needle intothe adjacent tissue.

With reference to the embodiments shown in FIGS. 20 and 21, balloon 55,which is made of polyvinylidene fluoride (PVDF), has a number of smallapertures 398 in the wall of the balloon. The inside of balloon 55 isconnected to a source of a drug by means of a lumen extending throughcatheter sheath 12d. Apertures 498 are force fed with the drug while theballoon material is caused to vibrate. The vibrations feed the transferof the fluid from balloon 55 into tissue with which the balloon is incontact. Radiopaque markers 410 and 412 are provided on catheter sheath12d.

Referring still to FIGS. 20 and 21, PVDF is a material that is similarto mylar and can be fabricated in sheets and then formed into balloonsthat have wall thicknesses in the range from 1-2 thousands of an inch.In order to permit excitation of the balloon wall, the PVDF material hasto be aluminized inside and out with aluminum layers 400. A very thinlayer of aluminization is all that is needed because the electricallyexcitable balloon 55 is a high impedance device. During use, analternating electric current is applied to balloon 55 at frequencies inthe kilohertz to megahertz range (the frequency depending on thethickness of the balloon and the mode of excitation). The electriccurrent causes the balloon to exhibit either transverse or planarvibration, which is therapeutically helpful in speeding the delivery ofdrugs and fluid into adjacent tissue. The vibration creates localizedvariations in pressure in the tissue, and given that fluid tends tomigrate in the direction of areas of low pressure, the vibration helpsmigration of fluid through the tissue. The vibration also can createheat, which is known to improve the diffusion of some chemicals throughtissue. Very high levels of vibration can be used as a massaging actionto actually disrupt tissue and to directly create an ablative response.

Referring to FIG. 22, a plan view of an acoustic imaging ballooncatheter system is shown. This acoustic imaging balloon catheter systemmay include all of the features of the catheter system shown in FIGS.19-19c, including one or more electrodes for electrophysiology orablation mounted on the catheter sheath. The system 120 includes a bootmember 122 including a ferrule member 124 at its proximal end,constructed to enable electrical and mechanical connection, as discussedfor example with respect to FIGS. 8-8a, to the acoustic imaging controlsystem as discussed for example with respect to FIG. 1, for transmittingrotary power and control signals to the acoustic imaging transducer heldwithin the balloon catheter sheath 139 near balloon 140 and forreceiving acoustical image signals from the transducer. The proximal endof the apparatus further includes a seal 126 (FIG. 23) which enablesintimate but relatively frictionless contact with the portion of therotating drive shaft.

Sheath 128 extends from the end of the seal 126 to a "Y" double flarecompression fitting 130. Fitting 130 includes a side arm 132 forintroduction of inflation fluid such as water or saline by means of ascrew syringe 134 for inflation of balloon 140 near the distal end ofthe catheter 139.

Extending distally from the compression fitting 130 is catheter bodysheath 139. The catheter may be adapted to track a guide wire whichpasses through a sonolucent saddle member beneath the balloon.

A rotating ultrasound transducer having a coil form drive shaft, asdiscussed herein above, is positioned on the central axis of thecatheter sheath 139 at a position corresponding to the inflatableballoon 140. The catheter sheath 139 forms a sonolucent guide for thetransducer and drive shaft. The catheter sheath is formed of a thinsonolucent material such as polyethylene to provide sufficient guidancefor the drive shaft and transducer without causing excessive attenuationof the ultrasound signal emitted by the transducer. The catheter bodymaterial and the balloon material are in general selected to besonolucent and have an acoustic impedance substantially matched to thebody fluid, e.g., blood, to which the catheter is exposed, to minimizeattenuation of the acoustic signals emitted and received from thetransducer. Polyethylene is advantageous in that it has an acousticimpedance that substantially matches blood and saline, it is capable ofwithstanding high inflation pressures and is only slightly elastic,enabling a reliable balloon inflation diameter. It will be understoodthat the catheter may be formed having sonolucent regions correspondingto the location of the transducer while the rest of the catheter is notsonolucent, e.g., made of thicker material. Fluid communication betweenthe balloon and the catheter may be provided through a port.

The balloon 140 which is preferably polyethylene, as discussed, may bemounted at its ends by, for example, melt-sealing. The balloon may alsobe secured by clips or the like as conventionally known.

Referring to FIG. 23, proximally, the catheter of FIG. 22 is providedwith a stationary pressure tight shaft seal 126 that fits in intimate,but relatively frictionless contact with a portion of the rotating driveshaft 162. The seal includes a ball seal 170 (available from Bal-sealEngineering Company, Inc., Santa Anna, Calif.), securely held in placeby a seal holder 172 (stainless steel or elastomer), which abuts thedistal end of the internal open area of the boot 122 and is held bycompression of the ferrule assembly 164 (although other means ofattachment such as injection molding are possible). The seal holder 172includes a retainer sleeve 174 that extends coaxially with respect tothe catheter 139. At the proximal end, within the ferrule, the driveshaft is held within a gland 178, preferably formed from hypotubing,which makes relatively frictionless contact with the ball seal 170,enabling rotation while preventing back flow of inflation fluid into theferrule. The ball seal, as shown, is an annular U-shaped member,including within the U a canted coil spring 179 (such that the axis ofeach coil is tangent to the annulus) that presses the legs 175, 177 ofthe seal radially. The outer leg 175 of the seal engages an extension176 of the seal holder, while the inner leg 177 of the seal engages thegland 178. The boot also includes a thin (few thousands of an inch)metal sleeve 171 for additional sealing around the catheter.

The drive shaft 162 is modified in the sealing area 168 by impregnatingit with a thermoplastic material that fills the gaps in the individualwires to prevent flow of inflation fluid through the drive shaft innerlumen. Alternatively, the drive shaft may be sealed by impregnating itwith a liquid that is hardenable, such as epoxy, and then covering thatarea with a section of cylindrical metal, such as hypotube, in order toform a smooth, fluid tight seal. It will also be understood that othersealing members may be used, e.g. an O-ring.

Preparation of the device is accomplished by the following steps: ALeveen inflator is connected to the side arm. The side arm valve isopened and air is evacuated by suction. Generally, the balloon contractsin a folded manner which leaves air passages through the interior of theballoon. A hypodermic syringe fitted with a small gauge needle andfilled with a fluid such as water or saline is then inserted through aseptum seal at the distal tip of the catheter sheath. Fluid isintroduced until surplus exits the side arm, at which point the valve isclosed, reducing the chances that air will re-enter the catheter.Alternately, the fluid may be introduced via the side arm when an airventing needle is inserted into the distal septum.

The catheter is then attached to the driving motor, (not shown), bymating the ferrule 124 with a mateable receptacle that connects it tothe ultrasound imaging electronics. Because the balloon material andsonolucent guide effectively transmit ultrasound energy, continuousimaging and monitoring can be achieved.

The pressure and fluid tight connector that is mounted distally to thelocation of the side arm connector enables various catheters, such asthose with balloons of different sizes, to be effectively attached atthe location of the side arm connector.

In other embodiments, the transducer may be positioned proximal to theballoon.

Referring now to FIGS. 24, 25, and 26, other embodiments of the acousticimaging catheter device allow relative movement of the transducer andballoon so that the ultrasound transducer may be positioned in anylongitudinal position in the balloon, or distal or proximal to theballoon. The embodiments shown in FIGS. 24, 25, and 26 may include allof the features of the catheter system shown in FIGS. 19-19c, includingone or more electrodes for electrophysiology or ablation mounted on thecatheter sheath, and may include all of the features of the cathetersystem shown in FIGS. 22 and 23. Moreover, the features shown in FIGS.24, 25, and 26 may be used in conjunction with any of the cathetersheaths disclosed in this application, including catheter sheaths thatdo not include balloons and including all of the catheter sheaths onwhich electrophysiology or ablation electrodes are mounted. In FIG. 24,the drive shaft and transducer 146 may be slid axially as indicated byarrows 195 to move the transducer, for example, continuously topositions between position I, proximal to the balloon and position II,distal to the balloon. A slide assembly 240 is provided including ahousing 244 having a distal end which receives the catheter sheath 139and drive shaft 145. The drive shaft contacts a pair of oppositelyarranged, relatively frictionless ball seals 245, 246 press fit withinthe housing against an inner body extension 249 and the distal endmember 248 of the body which is threaded into the body 244. The ballseals engage a gland 250 as discussed with respect to FIG. 23. The glandis attached to a thumb control 252, provided within the body to enableaxial motion of the drive shaft to position the transducer within thecatheter corresponding to regions within the balloon and in the distalextension, both of which are sonolucent.

The axially translatable transducer device further includes a carbonresistor 254 within the slide assembly housing, and contact means 258attached to the thumb control and in contact with the resistor. Probewires 256, 257 are connected to the resistor 254 and contact means 258to provide variable resistance between the probe wires as the thumbcontrol is slid axially, which is detected at detector 260, to providemonitoring of the axial position of the transducer. The thumb controlmay be hand actuated or controlled by automatic translator means 264which receives control signals from a controller 266. The output fromthe detector 260 may be provided to an analysis means 268 which alsoreceives the acoustic images from the transducer corresponding tovarious axial positions of the transducer within the catheter body toprovide registry of the images with the axial transducer position on ascreen 270. In certain embodiments, the transducer is slid axially,along a continuous length or at selected positions of the catheter body,for example, from the balloon to the distal tip, and the analysis meansincludes storage means for storing images along the length toreconstruct a three-dimensional image of the lumen along the axiallength of transducer travel.

FIG. 25 shows an embodiment in which the catheter includes a bellowsmember 280 to enable axial motion of the catheter body with respect tothe transducer.

FIG. 26 shows an embodiment in which a proximal portion of the driveshaft is enclosed within tubing 360, which is engaged by auser-graspable housing 362 that is attached to the proximal end ofcatheter sheath 364. The user can push tubing 360 into housing 362 andcan pull it out of housing 364 to adjust the relative longitudinalposition of the transducer on the end of the drive shaft with respect tocatheter sheath. User-graspable housing 362 engages tubing 360 by meansof a fluid-tight seal.

In another embodiment of the acoustic imaging catheter device, theballoon is asymmetrical, either in shape or expansion capability, orboth, and is mounted on a catheter shaft that is torquable, and can bepositioned using acoustic imaging. The positioning of the balloonrelative to surrounding tissue and the inflation and deflation of theballoon can be monitored with cross-sectional ultrasonic images.

FIGS. 27 and 27a show sheath 12b having needle 86 securely anchored tothe tip, useful for impaling a surface, such as that found in theinterior of the heart, and injecting chemicals such as ethanol into theheart. Needle 86 can also be used to anchor temporarily and steady theultrasound device in a fixed position. In another embodiment, it canhave a safety wire extending to a proximal securing point. This acousticcatheter may be introduced through an introducing catheter. In anotherembodiment, the needle can be retracted during introduction.

FIGS. 28 and 28a show a solid needle 324 made of an electricallyexcitable material that emits acoustic energy when excited throughconductor 326 by RF electrical signals applied to electrical terminal328. Vibration of needle 324 creates a massaging action that disruptstissue and creates an ablative response.

In an alternative embodiment, needle 324 is hollow, and the vibration ofthe needle assists the process of injecting the drug into the tissue.The hollow metal is covered with a shrink of polyvinylidene fluoride,and the polyvinylidene fluoride is aluminized over its outside. Thisconstruction produces an assembly that vibrates when electricallyexcited. The purpose of the aluminum is to conduct electric power. Thealuminum can be seen in the image formed by means of the ultrasoundtransducer, and it can also serve as an acoustic marker that can be seenby an external ultrasound device or an ultrasound probe placed adistance away from the ablation catheter.

FIGS. 29 and 29a show steerable catheter sheath 312, capable ofelectrophysiology sensing and acoustic imaging, in which the tip ofretractable injecting needle 314 exits catheter sheath 312 near the tipof the catheter sheath and also near ring electrode 316 and the positionof the scan plane of transducer 318. Visualization of the location ofthe electrode can be performed under ultrasound guidance, and then theneedle can be extended into the endocardium to inject fluid into theendocardium. Electrode 316 is the most distal of several electrodes 316,320, and 322. Ring electrode 316 may be of a conventional type that canbe located with ultrasound. In another embodiment electrode 316 is a tipelectrode rather than a ring electrode.

In one embodiment, the longitudinal position of the transducer isadjustable, in accordance with any of the techniques described above inconnection with FIGS. 24, 25, and 26. In another, simpler embodiment,transducer 318 is located permanently in a fixed longitudinal locationat which the plane of acoustic imaging intersects the needle when theneedle at the beginning of its extended position.

In use, the catheter is put into position in the heart with needle 314retracted, a site that is suspected of electrical malfunction is probedwith the steerable catheter under ultrasound visualization, andelectrical potentials are read and recorded. Once a specific location isfound that appears to be problematic, ablation can then be performed bydeploying the needle and the needle can inject the tissue with anablative drug such as ethanol. The needle can penetrate 2-3 millimetersif necessary. The catheter can be left in position during this time anda change in the electrical properties of the tissue can be monitored.

In another embodiment, a highly conductive wire, such as gold-platedmetal or gold-plated stainless steel, can be used in place of theneedle. The wire ablates tissue in a manner analogous to the ablationelectrodes described above, but the wire can be used to anchor thecatheter and could be curved to pull the electrode into position toenhance the electrical ablation. The wire can include an acoustic markerthat can be seen by an external ultrasound device or an ultrasound probeplaced a distance away from the ablation catheter.

In certain embodiments, shown in FIGS. 30, 30a, 31, and 31a, the wire isformed as a little cork screw 402 that can be twisted into the heart, ina manner similar to twisting a pacing lead into the heart, to anchor thetip of catheter sheath 404 very securely under ultrasound guidance.FIGS. 30 and 30a show cork screw 402 directly attached to cathetersheath 404. In this embodiment cork screw 402 is twisted into hearttissue by rotating the entire catheter. FIGS. 31 and 31a show cork screw402 directly attached to drive shaft 406, distally beyond transducer408. In this embodiment cork screw 402 is twisted into heart tissue byrotating drive shaft 406. In other embodiments, the corkscrew isattached to an elongated, torsionally rigid but laterally flexibleassembly, similar to the ultrasound imaging driveshaft but much smallerin diameter, so that the corkscrew can be automatically caused to turnand corkscrew into tissue. The corkscrew exits a small hole in thecatheter sheath in the same manner as needle 314 described above, butthe corkscrew follows a curved path.

Referring to FIGS. 32 and 32a, in catheter sheath 418, an ultrasoundtransducer 414 is used to ablate tissue sonically. Ultrasound transducer414 is similar to, and located adjacent to, ultrasound imagingtransducer 416 of the type described in detail above. Transducer 416images by rotating a full 360 degrees while catheter sheath 418 is in afixed position or a relatively stationary position, the image is stored,and then the rotation of the transducer is stopped and the position oftransducer 414 is aligned, based on the stored image, so that transducer414 is pointed toward the region of interest. During ablation,transducer 414 radiates at least 2-5 watts of acoustic power at afrequency of around 25 to 50 kilohertz. This frequency that is so lowthat the radiation is not focused, but instead tends to radiate from thesource in a more or less cardioid pattern without a fixed focus. Theenergy has its greatest density normal to the surface of transducer 414.

In another embodiment the ablation transducer is positioned in a mannersuch that it directs radiation in a direction 180 degrees away from thedirection in which the imaging transducer directs ultrasound energy, andthe ablation transducer and imaging transducer are at the samelongitudinal location. The ablation transducer can be aligned in thedesired direction for ablating tissue by positioning the imagingtransducer in a manner such that the imaging transducer is facing 180°away from the region of interest to be ablated. In yet anotherembodiment a single transducer is capable of both imaging and veryhigh-power, low-frequency radiation.

FIG. 33 illustrates an alternative imaging mode that is useful inconjunction with the needle-equipped and balloon-equipped catheters forchemical ablation described above, and also even the electrode-equippedcatheters described above, if the electrodes are fitted withpolyvinylidene fluoride coverings. According to this imaging mode, theheart 352 is imaged through the esophagus 354, by means of one of manycommonly available trans-esophageal probes 356 such as those made byHewlett Packard, Vingmead and others. This trans-esophageal imagingprovides a cross-sectional image of the heart, i.e., a scan plane thatis a slice of the heart. Various improved trans-esophageal probes canvary the plane scanned through the heart through various angles andvarious rotational and azimuthal positions, and can therefore be used toimage a very wide area of the heart through manipulation of controls onthe proximal end of the transesophageal probe. During use,transesophageal probe 356 is first placed in a patient's esophagus priorto the beginning of an electrophysiology procedure, andelectrophysiology or ablation catheters 358 and 359 are then placed inthe heart through the venous or the arterial system. These catheters canbe visualized by means of esophageal probe 356 if the catheters arefitted with acoustic markers.

The marker may be, for example, a PVDF covering placed over a sensing orablation electrode, or a PVDF balloon. The acoustic markers are used tocreate distinct color artifacts on the image created by color flowimaging machines equipped with color capability. The color flow displayis a black and white display that has a graphic overlay of flowinformation, which is denoted by a color shown on the CRT display. Whenthe PVDF is electrically excited it emits a low-frequency sonic wavethat is misinterpreted by the trans-esophageal imaging system as thedifference between the outgoing ultrasound pulse and the Doppler-shiftedreturn pulse that the trans-esophageal system uses to deduce thedirection and quantity of blood flow (the imaging system determinesblood flow by measuring the difference between the outgoing and theincoming ultrasound signal and assigning a false color to the frequencyshift that occurs due to the Doppler effect). Thus, by radiating at afrequency near the expected Doppler shift frequency, the PVDF basicallyfools the trans-esophageal imaging system into thinking thelow-frequency sonic wave is the difference signal and can induce theimaging system to show false colors that identify particular catheters.A catheter shows up on the display as either a bright mark or dot thatrepresents the cross-section of the catheter. To energize the PVDF asinusoidal, continuous-wave, voltage signal is applied to the PVDFthrough a simple, alternating-current, radio-frequency generator. Thissignal can be pulsed as well, if desired.

One or more of the intra-cardiac catheters may include an ultrasoundtransducer, which may be adjacent to or at the precise location ofsensing and ablation electrodes, as described above. Vacuum-depositedtraces may extend along the length of the catheter sheath to theelectrodes, as described above. The traces provide good electricalcoupling and can serve as an attachment point for PVDF or a crimped-ontransducer. The incorporation of the traces into the wall of thecatheter sheath leaves the bore of the catheter free to be used for apacing lead, an anchoring screw, a drug injection channel, a biopsychannel, etc.

In one embodiment, an entire catheter sheath is made of PVDF. Thecatheter sheath will show up on the display no matter which portion ofthe catheter sheath intersects with the imaging plane of thetransesophageal probe, because the whole catheter sheath emanatesradiation. In another embodiment, a first catheter used during theprocedure emits a frequency that shows up as a first color on the colorflow imaging, a second catheter emits a frequency that shows up as asecond color, and so on. In another embodiment the tip or the actualelectrode portion of a catheter sheath has a frequency that is distinctfrom the rest of the catheter sheath, so that when the tip or theelectrode is located by the imaging system it is distinguishable fromthe remainder of the catheter sheath. In another embodiment, there is agraduation in frequency along the length of a catheter, so that a distaltip shows up as a first color, a midsection shows up as a second color,and a proximal section shows up as a third color. The change infrequency along the length of the catheter may be gradual or may be inthe form of distinct stripes of different frequencies.

FIG. 34 illustrates a system of electrophysiology equipment thatincludes an acoustic imaging electrophysiology catheter 368 of the typeshown in FIG. 13, a trans-esophageal probe 370, a central processingunit 372 that receives data from catheter 368 or trans-esophageal probe370 and transmits video ultrasonic image data to ultrasound display 374,and another display system 376 that displays, either graphically,schematically, or with a wire frame, specific regions of the heart, andthat records and displays on a specific location of the graphical,schematic, or wire frame display either an instantaneous voltage or avoltage throughout an entire cardiac cycle.

In one embodiment, display system 376 displays a two-dimensionalcross-sectional image of the heart, which shows important features ofthe heart such as the area of the HIS bundle. The cross-sectional imageis based on ultrasound image received from catheter 368 ortrans-esophageal probe 370 or is based on a fluoroscopic image fromfluoroscope 382. Other possible sources of the cross-sectional imageinclude MRI, CT, and scintigraphy. When catheter 368 is placed inspecific regions of the heart, which can be done with great certaintybecause of the ultrasound imaging capability, the voltage potentialssensed by catheter 368 are recorded instantaneously by centralprocessing unit 372 and then displayed in the specific locations in thegraphic. Many voltage potentials are sensed at various locations in theheart until an electrophysiological map of the heart is built up, whichcan be done very quickly.

Because the user or the clinician will want to concentrate onmaneuvering the catheters, and not on data acquisition, writinginformation down, or shouting out numbers, a foot pedal 378 is providedso that when catheter 368 is in a specific location the clinician candepress foot pedal 378 to instruct central processing unit 372 to recordvoltage potential information. Because central processing unit 372receives ultrasound imaging data, central process unit 372 knows thespecific location of each electrophysiology electrode and thus knows thelocation at which to super-impose voltage data on the image shown bydisplay system 376. Alternatively, the clinician can observe the imagedisplayed by display system 374 and can indicate to central processingunit 372 the specific location of an electrode.

Thus, central processing unit 372 records both an ultrasonic image at aparticular instant and a voltage values at that instant and at aparticular location. Thus, the clinician can return the sensingelectrode to the particular location at a later point in time to comparethe voltage sensed at the later point in time with the earlier-recordedvoltage.

Moreover, the information recorded by central processing unit 372permits analysis of various voltage potentials throughout a cardiaccycle as the heart moves during the cycle, because central processingunit 372 is able to keep track of the various locations in the hearteven though the heart is moving.

A set of electrocardiogram or EKG leads 380 are connected to centralprocessing unit 372. In one embodiment, when the clinician wants torecord a voltage potential, central processing unit 372 records thevoltage information throughout one complete cardiac cycle. The cliniciancan view a representation of the voltage at any instance in time duringthe cardiac cycle by replaying the image displayed by display system 376with the super-imposed voltage information. Central processing unit 372processes ultrasound imaging information and voltage information in themanner of a cine loop or repeating image, which is gated by EKG leads380 attached to the patient while the patient is left in a stillposition. The central processing unit causes display system 376 todisplay a series of successive frames in a loop that repeats over andover again. In one embodiment there are 32 ultrasound imaging framesthat go through one complete cardiac cycle from systole to diastole andback to systole, and there are 32 different voltages that aresuper-imposed on the ultrasound imaging frames at any given location.The super-imposed voltage information at a given location is a numberthat rises and falls throughout the cardiac cycle, or is alternatively acolor coded mark. Thus, there is no need to image the heartcontinuously, which could take up a lot of software and hardware time,and yet display system 376 displays an image of the heart timed in exactsynchronization with the actual heart beating (through use of EKG leads380) and replayed over and over again. While this image is beingreplayed, the clinician can concentrate on simply locating the positionof catheter 368 itself in the heart and can follow the catheter withtrans-esophageal echo probe 370, or through x-rays because catheter 368is marked with radiopaque markers.

Any additional information that the clinician obtains while the image isbeing replayed can be super-imposed over the repeating image without theneed to re-image the heart. For example, a live fluoroscopic orultrasound image can be super-imposed over the image being replayed ondisplay system 376. If the super-imposed live image is a fluoroscopicimage, it is not necessary to use dye injection while obtaining thislive image because the location of the heart tissue relative to thecatheter 368 can be seen on display system 376 without any need for thelive image itself to show the heart. If the clinician wishes, however,he may update the image by obtaining a new image of the heart, if thepatient has moved or if the clinician believes that the heart haschanged position or has changed its cycle.

In another embodiment, the display system 376 displays a falsethree-dimensional image of the heart or a true three-dimensional imageof the heart. A false three-dimensional image of the heart is athree-dimensional projection onto a two-dimensional surface that can begenerated using commonly available computer imaging hardware andsoftware that takes a number of successive two-dimensional images andassembles them into a false three-dimensional image that can be rotatedand manipulated by the user by the user interfacing with centralprocessing unit 372. False three-dimensional ultrasound images can beobtained through the use of accessory software and hardware such as thatprovided by ImageComm in Sunnyvale, Calif. A true three-dimensional isan image that is not displayed on a flat screen but rather on anoscillating mirror that has a scanning system associated with it thatcan display a three-dimensional image by stereoscopic means. It is notnecessary to wear stereoscopic glasses to view oscillating mirrorsystems that are currently being marketed.

Alternatively, display system 376 may display a wire-frame image, whichis a graphical depiction of the boundaries of the heart and is a simpleversion of a false 3-dimensional image. The beauty of a wire frame imageis that it requires relatively less software and hardware to display andis inherently transparent or translucent so that potentials can be seenthrough it intuitively by the user. Also, a wire-frame images does notrequire a large amount of hardware or software to rotate and manipulatethe image. The nodal points, i.e. the places where the wires cross, canbe used as the data collection points.

One of the very important aspects of the electrophysiology procedure isthat once the operation of the heart is diagnosed, the clinician willwant, as precisely as possible, to position an ablation device at thesource of trouble and ablate the tissue at this location precisely. Thisrequires relocalization of the tip of catheter 368 to a previouslylocated position. All positions at which the catheter tip has beenpositioned are accurately located on the display of display system 376,and the clinician can determine when the tip of catheter 368 has beenrelocated by examining the ultrasound image. Thus, the clinician canreturn to the spot to be ablated with a great degree of confidence.

In one embodiment, trans-esophageal probe 370 creates ultrasound imagesthat are processed by central processing unit 372 and displayed bydisplay system 376, and the ultrasound transducer on catheter 368 isused to create an image displayed on display system 374 to assure goodcontact of electrodes with tissue. Alternatively, a general sense of thecatheter position is obtained through the use of an imaging modalitysuch as fluoroscope 382, and a more precise image is obtained bytrans-esophageal probe 370 or the ultrasound transducer on catheter 368and is processed by central processing unit 372 to create the displayfor display system 376.

The electrophysiology catheters described in detail above are especiallyuseful for creating an accurate two-dimensional, three-dimensional, orwire-frame image because these catheters are highly maneuverable bytheir ability to deflect or to be positioned with the assistance of apositioning balloon, because the transducer within these catheters ishighly accurate in identifying the position of the catheter relative totissue, and because these catheters are easily recognizable intrans-esophageal images.

A data recorder 384 is provided in the system of electrophysiologyequipment shown in FIG. 34 to record data from EKG leads 380 and theelectrophysiology electrodes on catheter 368 in tabular form foranalysis. An oscilloscope 388 displays signals from each of theelectrophysiology electrodes on catheter 368. A programmable externalstimulator 386 is used to provide slight electrical pulses to electrodeson catheter 368 to cause fibrillation so that the action of the heartcan be observed while the heart is in this condition.

Other embodiments are within the claims. For example, it is contemplatedthat each of the various selectable catheter sheaths may incorporate anyof the features shown or described in connection with one or more of theother selectable catheter sheaths. Furthermore, the ultrasoundtransducer described above may be used in conjunction with cathetersheaths incorporating the features of any of the catheters described ineither of the following two U.S. patent applications, which are beingfiled on the same day as the present application, and the disclosures ofwhich are hereby incorporated in their entirety herein: "AblationCatheters," by Charles D. Lennox et al., and "Heart Ablation Catheterwith Expandable Electrode" by John E. Abele.

It is contemplated that each of the various selectable catheter sheathsmay be used in conjunction with any of the technologies shown in FIGS.24, 25, and 26 for enabling relative longitudinal movement between thetransducer and the catheter sheath during use of the catheter. Also,each of the various selectable catheter sheaths may be used inconjunction with a drive shaft of the type shown in FIG. 35, in whichdrive shaft 342 has a rotating mirror 344 on its distal end thatreflects an ultrasound signal emitted by an ultrasound transducer 346,which may also be attached to drive shaft 342 as shown or alternativelymay be fixed in a stationary position while the drive shaft rotates.

What is claimed is:
 1. An acoustic imaging system for use within a bodyof a living being, comprising:an elongated, flexible catheterconstructed to be inserted into said body of said living being, anultrasound device movable within said elongated, flexible catheter, achemical ablation device mounted on a distal portion of said elongated,flexible catheter, and a plurality of electrical conductors extendingfrom a proximal portion of said elongated, flexible catheter to saiddistal portion, at least two of said plurality of electrical conductorsbeing connected to said ultrasound device, said ultrasound device beingarranged to direct ultrasonic signals toward an internal structurewithin said body of said living being for the purpose of creating anultrasonic image of said internal structure, and said chemical ablationdevice being arranged to ablate at least a portion of said internalstructure imaged by said ultrasound device by delivery of fluid to saidinternal structure, said chemical ablation device being arranged tocause ablation solely by fluid delivery only.
 2. An acoustic imagingsystem in accordance with claim 1, wherein said ablation devicecomprises a needle constructed to inject a fluid into said internalstructure of said body of said living being.
 3. An acoustic imagingsystem in accordance with claim 2, wherein said needle extends from thedistal tip of said catheter.
 4. An acoustic imaging system in accordancewith claim 2, wherein said needle extends from a side wall of saidcatheter.
 5. An acoustic imaging system in accordance with claim 2,wherein at least a portion of said needle is within a plane defined bysaid ultrasonic signals directed by said ultrasound device toward saidinternal structure of said body of said living being.
 6. An acousticimaging system in accordance with claim 2, wherein:said acoustic imagingsystem further comprises an electrophysiology electrode, and said needleis located in the vicinity of said electrophysiology electrode.
 7. Anacoustic imaging system in accordance with claim 2, wherein said needlehas a retracted position and an extended position and is movable betweensaid retracted position and said extended position.
 8. The acousticimaging system recited in claim 1 wherein the ultrasonic device isrotatably disposed within the catheter.
 9. The acoustic imaging systemrecited in claim 8 wherein the catheter is elongated along alongitudinal axis and wherein the ultrasonic device is disposed forrotation within the catheter about the longitudinal axis.
 10. Anacoustic imaging system for use within a body of a living being,comprising:an elongated, flexible catheter constructed to be insertedinto said body of said living being, an ultrasound device movable withinsaid elongated, flexible catheter, a chemical ablation device mounted ona distal portion of said elongated, flexible catheter, and a pluralityof electrical conductors extending from a proximal portion of saidelongated, flexible catheter to said distal portion, at least two ofsaid plurality of electrical conductors being connected to saidultrasound device, said ultrasound device being arranged to directultrasonic signals toward an internal structure within said body of saidliving being for the purpose of creating an ultrasonic image of saidinternal structure, and said chemical ablation device being arranged toablate at least a portion of said internal structure imaged by saidultrasound device by delivery of fluid to said internal structure,wherein said ablation device comprises a balloon having a wall withports for delivery of fluid to said internal structure of said body ofsaid living being.
 11. An acoustic imaging system in accordance withclaim 10, wherein said balloon is sonolucent.
 12. An acoustic imagingsystem in accordance with claim 11, wherein at least a portion of saidballoon is within a plane defined by said ultrasonic signals directed bysaid ultrasound device toward said internal structure of said body ofsaid living being.
 13. An acoustic imaging system for use within a bodyof a living being, comprising:an elongated flexible catheter constructedfor insertion into said body, an ultrasonic device incorporated intosaid elongated, flexible catheter, a chemical ablation device mounted ona distal portion of said elongated, flexible catheter and a plurality ofelectrical conductors extending from a proximal portion of saidelongated, flexible catheter to said distal end portion, at least two ofsaid plurality of electrical conductors being connected to saidultrasonic device, said ultrasonic device being arranged to directultrasonic signals toward an internal structure within said body of saidliving being for the purpose of creating an ultrasonic image of saidinternal structure, and said chemical ablation device being arranged toablate at least a portion of said internal structure imaged by saidultrasonic device by delivery of fluid to said internal structure,wherein said ablation device comprises a balloon having a wall withports for delivery of fluid to said internal structure of said body ofsaid living being, and, wherein said balloon comprises a material thatvibrates in response to electrical excitation, at least two of saidplurality of electrical conductors being connected to said material tocause vibration thereof, said delivery of said fluid to said internalstructure being assisted by vibration of said material.
 14. An acousticimaging system for use within a body of a living being, comprising:anelongated, flexible catheter constructed for insertion into said body,an ultrasonic device incorporated into said elongated, flexiblecatheter, a chemical ablation device mounted on a distal portion of saidelongated, flexible catheter and a plurality of electrical conductorsextending from a proximal portion of said elongated, flexible catheterto said distal end portion, at least two of said plurality of electricalconductors being connected to said ultrasonic device, said ultrasonicdevice being arranged to direct ultrasonic signals toward an internalstructure within said body of said living being for the purpose ofcreating an ultrasonic image of said internal structure, said catheterbeing adapted to have a surface portion thereof contact said internalstructure, said chemical ablation device being arranged with thecatheter to introduce a chemical ablative fluid into the contactedinternal structure immediately as said fluid leaves the chemicalablative device, said chemical ablation device being arranged to ablateat least a portion of said internal structure imaged by said ultrasonicdevice by delivery of fluid to said internal structure, said chemicalablation device being arranged to cause ablation solely by fluiddelivery only.
 15. The acoustic imaging system recited in claim 14wherein the catheter and the chemical ablation device are a single unit.16. The acoustic imaging system recited in claim 15 wherein the chemicalablation device is needle shaped having a pointed distal portion and ahollow proximal portion, and wherein the catheter has a hollow distalend portion coupled to the hollow proximal portion of the needle shapedchemical ablation device, and wherein the fluid is disposed in thehollow distal end portion and passes to the hollow proximal portion assuch fluid leaves the chemical ablation fluid passes to the internalstructure.
 17. The acoustic imaging system recited in claim 17 whereinthe catheter has a needle-shaped tip at the distal end thereof.
 18. Anacoustic imaging system for use within a body of a living being,comprising:an elongated, flexible catheter constructed for insertioninto said body, an ultrasonic device incorporated into said elongated,flexible catheter, a chemical ablation device mounted on a distalportion of said elongated, flexible catheter and a plurality ofelectrical conductors extending from a proximal portion of saidelongated, flexible catheter to said distal end portion, at least two ofsaid plurality of electrical conductors being connected to saidultrasonic device, said ultrasonic device being arranged to directultrasonic signals toward an internal structure within said body of saidliving being for the purpose of creating an ultrasonic image of saidinternal structure, said chemical ablation device being arranged toablate at least a portion of said internal structure imaged by saidultrasonic device by delivery of fluid to said internal structure, saidchemical ablation device being arranged to cause ablation solely byfluid delivery only, and wherein the catheter and the chemical ablationdevice are a single unit.
 19. The acoustic imaging system recited inclaim 18 wherein the chemical ablation device is needle shaped having apointed distal portion and a hollow proximal portion, and wherein thecatheter has a hollow distal end portion coupled to the hollow proximalportion of the needle shaped chemical ablation device, and wherein thefluid is disposed in the hollow distal end portion and passes to thehollow proximal portion as such fluid leaves the chemical ablation fluidpasses to the internal structure.
 20. The acoustic imaging systemrecited in claim 19 wherein the catheter has a distal end tip andwherein the needle shaped is disposed at the tip.
 21. A method ofacoustically imaging a body of a living being, comprising:(a) providingan elongated, flexible catheter constructed for insertion into saidbody, said catheter comprising:(i) an ultrasonic device incorporatedinto said elongated, flexible catheter, (ii) a chemical ablation devicemounted on a distal portion of said elongated, flexible catheter and(iii) a plurality of electrical conductors extending from a proximalportion of said elongated, flexible catheter to said distal end portion,at least two of said plurality of electrical conductors being connectedto said ultrasonic device, (b) directing ultrasonic signals toward aninternal structure within said body of said living being for the purposeof creating an ultrasonic image of said internal structure, and (c)introducing a chemical ablative fluid into the contacted internalstructure immediately as said fluid leaves the chemical ablative deviceto ablate at least a portion of said internal structure by fluiddelivery only.
 22. An acoustic imaging system for use within a body of aliving being, comprising:an elongated, flexible catheter constructed tobe inserted into said body of said living being, an ultrasound devicelongitudinally displaceable within said elongated, flexible catheter, achemical ablation device mounted on a distal portion of said elongated,flexible catheter, and a plurality of electrical conductors extendingfrom a proximal portion of said elongated, flexible catheter to saiddistal portion, at least two of said plurality of electrical conductorsbeing connected to said ultrasound device, said ultrasound device beingarranged to direct ultrasonic signals toward an internal structurewithin said body of said living being for the purpose of creating anultrasonic image of said internal structure, and said chemical ablationdevice being arranged to ablate at least a portion of said internalstructure imaged by said ultrasound device by delivery of fluid to saidinternal structure, said chemical ablation device being arranged tocause ablation solely by fluid delivery only.
 23. An acoustic imagingsystem for use within a body of a living being, comprising:an elongated,flexible catheter constructed to be inserted into said body of saidliving being, an ultrasound device incorporated into said elongated,flexible catheter, a chemical ablation device mounted on a distalportion of said elongated, flexible catheter, and a plurality ofelectrical conductors extending from a proximal portion of saidelongated, flexible catheter to said distal portion, at least two ofsaid plurality of electrical conductors being connected to saidultrasound device, said ultrasound device being arranged to directultrasonic signals toward an internal structure within said body of saidliving being for the purpose of creating an ultrasonic image of saidinternal structure, and said chemical ablation device being arranged toablate at least a portion of said internal structure imaged by saidultrasound device by delivery of fluid to said internal structure, atleast a portion of said chemical ablation device being within a planedefined by said ultrasonic signals directed by said ultrasound devicetoward said internal structure of said body of said living being.
 24. Anacoustic imaging system for use within a body of a living being,comprising:an elongated, flexible catheter constructed to be insertedinto said body of said living being, an ultrasound device incorporatedinto said elongated, flexible catheter, a chemical ablation needlemounted on a distal portion of said elongated, flexible catheter andextending from a side wall of said catheter, said chemical ablationneedle being constructed to inject fluid into an internal structure ofsaid body of said living being, and a plurality of electrical conductorsextending from a proximal portion of said elongated, flexible catheterto said distal portion, at least two of said plurality of electricalconductors being connected to said ultrasound device, said ultrasounddevice being arranged to direct ultrasonic signals toward said internalstructure within said body of said living being for the purpose ofcreating an ultrasonic image of said internal structure, and saidchemical ablation needle being arranged to ablate at least a portion ofsaid internal structure imaged by said ultrasound device by delivery offluid to said internal structure.
 25. An acoustic imaging system inaccordance with claim 24, wherein at least a portion of said chemicalablation needle is within a plane defined by said ultrasonic signalsdirected by said ultrasound device toward said internal structure ofsaid body of said living being.
 26. An acoustic imaging system inaccordance with claim 24, wherein said acoustic imaging system furthercomprises an electrophysiology electrode, and said chemical ablationneedle extends from said side wall of said catheter in the immediatevicinity of said electrophysiology electrode.
 27. An acoustic imagingsystem in accordance with claim 24, further comprising:a balloon mountedon a distal portion of said elongated, flexible catheter, said ballooncomprising a material that vibrates in response to electricalexcitation, and a plurality of electrical conductors extending from aproximal portion of said elongated, flexible catheter to said distalportion, at least two of said plurality of electrical conductors beingconnected to said material of said balloon to cause vibration thereofand thereby to assist delivery of said fluid injected by said needleinto said internal structure.
 28. An acoustic imaging system inaccordance with claim 27, wherein said needle is constructed to exitthrough a side wall of said balloon.
 29. A chemical ablation system foruse within a body of a living being, comprising:an elongated, flexiblecatheter constructed to be inserted into said body of said living being,a chemical ablation needle mounted on a distal portion of saidelongated, flexible catheter, said chemical ablation needle beingconstructed to inject fluid into an internal structure of said body ofsaid living being, and a balloon mounted on a distal portion of saidelongated, flexible catheter, said balloon comprising a material thatvibrates in response to electrical excitation, a plurality of electricalconductors extending from a proximal portion of said elongated, flexiblecatheter to said distal portion, at least two of said plurality ofelectrical conductors being connected to said material of said balloonto cause vibration thereof and thereby to assist delivery of said fluidinjected by said needle into said internal structure.
 30. A chemicalablation system in accordance with claim 29, further comprising anultrasound device incorporated into said elongated, flexible catheter,at least two of said plurality of electrical conductors being connectedto said ultrasound device, said ultrasound device being arranged todirect ultrasonic signals toward said internal structure within saidbody of said living being for the purpose of creating an ultrasonicimage of said internal structure, and said chemical ablation needlebeing arranged to ablate at least a portion of said internal structureimaged by said ultrasound device by delivery of fluid to said internalstructure.
 31. A chemical ablation system in accordance with claim 29,wherein said needle is constructed to exit through a side wall of saidballoon.